The top of my stomach is hard and the bottom is flabby. There is no pain but I do feel bloated. I have one kid and I am on a birth control implant that lasts 3 years and I'm on the third year. I feel like this is pregnancy but all tests are negative.

Could be normal. After pregnancy the bottom abdominal muscles are more stretched out than they were before. Sometimes the abdominal muscles are separated, called rectus diastasis. Either way, bloating from gas, hormones, and intestinal issues is more pronounced due to these issues. It is never wrong to see a doctor for an evaluation if there is a concern.